Dry describes what happened during fermentation, not how the wine tastes on its own. Yeast ate almost all the grape sugar and turned it into alcohol, so a dry red arrives in the glass with acid, tannin, and alcohol carrying the whole flavor and almost no sugar left to round any of it off. That absence is the reason a dry wine turns sharper rather than smoother the longer you reduce it in a pan.
What "dry" actually measures
Grape juice is full of sugar, and fermentation is yeast eating that sugar and excreting alcohol and carbon dioxide until it either runs out of food or poisons itself on its own alcohol. A winemaker who lets that process run to completion ends up with a dry wine — most finish with well under 10 grams of residual sugar per liter, and plenty of dry reds land closer to 1 or 2. Stop fermentation early, by chilling the tank or adding sulfur before the yeast finishes, and sugar gets left behind on purpose. That's the entire distinction. It has nothing to do with tannin, body, or alcohol content, even though people use "dry" loosely to mean all three.
Why tannin and acid do all the talking in a dry wine
Take the sugar cushion away and what's left is what the grape and the fermenting process actually put there. Tannins are polyphenols pulled out of grape skins, seeds, and stems while the juice sits fermenting with them — reds macerate on their skins far longer than whites, which is the entire reason reds carry more tannin. Those molecules bind to the proline-rich proteins in your saliva and drag them out of solution, and losing that slick protein layer is what registers as astringency, the puckering, drying sensation people mean when they call a wine "dry" at the table. Acid does the other half of the work. Wine runs at a pH around 3.3 to 3.7 — sharper than most food — mostly from tartaric acid the grape itself produced. With no sugar to soften either one, tannin and acid are the whole sensation.
Why reducing a bad bottle makes it worse, not better
Reducing a sauce boils off water and alcohol, and it does that indiscriminately — the pot doesn't know which molecules taste good. Whatever ratio of flavor to flaw existed in the bottle survives the reduction at the same ratio, just concentrated into less liquid. A wine that was thin or had a sharp, vinegary edge from excess volatile acidity doesn't lose that edge as it cooks down. It gets a smaller glass of the same problem. This is the actual mechanism behind "never cook with wine you wouldn't drink" — the saying isn't about wasting good wine on a pot, it's that heat has no way to fix what's already wrong with a bad one.
Why a long braise hides tannin that a quick reduction doesn't
Tannin doesn't care whether the protein it binds is sitting in your saliva or dissolved in a braising liquid. A dish like coq au vin or a long-braised pot roast releases collagen from the meat as it cooks for an hour or more, and that collagen turns to gelatin right in the sauce — protein tannin can grab onto before it ever reaches your tongue. A fast pan reduction, wine cooked down on its own for a steak sauce with nothing else in the pot, has no protein to soak any of that up. Same tannin, same acid, same reduction — the difference is what else is in the liquid while it happens.
How much alcohol is actually still there
Ethanol boils at 173°F (78°C), well below water's 212°F (100°C), which is why people assume it disappears fast. It doesn't, because it's fully dissolved in the water rather than sitting as a separate layer, so it leaves gradually as the whole pot reduces rather than flashing off at once. Stirred into a liquid and simmered for 15 minutes, a dish still holds around 40 percent of the alcohol that went in; at 30 minutes it's down to about 35 percent, and it takes something closer to two and a half hours of continuous cooking to get near 5 percent. Even flambéing barely touches it — the flame looks dramatic but leaves roughly three-quarters of the alcohol behind, because the burn only lasts seconds.
Why bottled "cooking wine" isn't the same product
The bottle labeled "cooking wine" sitting in the vinegar aisle isn't a lesser version of the wine next to it in the wine aisle — it's a different product built to be sold without the licensing regular wine needs. Salt gets added, often enough that it's unpleasant to drink on its own, which is what lets it skip age-verification and liquor laws in a lot of states. It's also usually made from cheaper base wine to begin with. Cook with it and you're adding sodium you have to account for everywhere else in the dish, on top of reducing a wine that had less to offer before it ever hit the pan.